Generally, a ball for ball game is mainly composed of a bladder which can be inflated with air and can maintain certain air pressure; an reinforcing layer which realizes the quality of a ball such as sphericity and durability; and a skin layer, i.e. a panel, located on the reinforcing layer. The game ball can be categorized into the following three main types based on different manufacturing methods: laminated balls, hand-stitched balls, and machine-stitched balls.
FIG. 1 shows a ball having a hole 5 for admitting inflating air, and leather panels 4. FIGS. 2 to 4 show sectional views of balls of different types taken along line A-A. FIG. 2 illustrates a laminated ball. As described in U.S. Pat. No. 4,333,648, several-thousand meters of fiber like nylon filament are wound around an impermeable rubber bladder 2 along all peripheral directions to form reinforcing layer 3. In the process for winding nylon filament, an adhesive is coated on the nylon filament to prevent it from sliding off. The reinforcing layer itself has the functions of maintaining the spherical shape and resisting impact. Leather panels 4 are attached to the reinforcing layer 3 using adhesive 11 to form the skin layer. In order to improve the adherability, the reinforcing layer 3 can be covered with rubber. As shown in FIG. 1, the leather panels 4 of the ball generally has 32 pieces including 12 pieces of regular pentagon and 20 pieces of regular hexagon. The material for the panel is genuine leather or artificial leather (with a thickness of 1.0-2.0 mm). The peripheral portion of the back of the leather panel 4 is cut obliquely, and a V-shaped groove 6 is formed on a leather panel joint, so that the V-shaped panel groove 6 for suppressing air resistance and improving flying property is formed. As known from this manufacturing method, the laminated ball has an integral structure in which the bladder 2, reinforcing layer 3 and leather panels 4 are attached to each other using adhesive. The arrows represent the air pressure in the bladder 6. Laminated balls with the above structure have high quality, good sphericity and small errors in size and weight, because they can be produced in mechanized way. And the balls have excellent durability because the reinforcing layer is made of nylon filament.
However, laminated balls have some disadvantages. The panel grooves 6 is too wide and too shallow, being approximately 8 mm in width and 1 mm in depth, so that air resistance is not sufficiently low. The disadvantages also include poor gripping property, hard tactility when kicked, and poor controlling properties, so that the balls can not be official game balls.
FIG. 3 illustrates a hand-stitched ball. In a hand-stitched ball, an unattached bladder 2 is accommodated in a skin pocket made of complex panels 9, so that it is in a free state. After the air is inflated in, the bladder 2, made of elastic rubber, is pressed against the inner surface of the complex panels 9 due to the inner air pressure (as indicated by arrows in FIG. 3). A leather panel 4 with a liner or buffering material attached to its back is generally referred to as a complex panel. The hand-stitched ball is generally formed in such a process that the liner material as the reinforcing layer 3 made of laminated 3-4 pieces of fabrics with adhesive is attached to the back of the leather panel 4 to form the complex panel 9, the complex panels 9 are stitched together using a hand-stitching thread 7 (about 10000-denier thread) to form the ball shell having spherical shape, and the bladder 2, the same as the one used in the above-mentioned laminated ball, is accommodated in the ball shell. The place where the complex panels 9 are stitched is shown in FIG. 3, and the bladder 2 has the same shape as that of the inner surface of the panels 9 after the ball is inflated. The leather panels 4 are made of the same genuine or artificial leather as used in the laminated balls (with a thickness of 1.0-2.0 mm). The ball with this kind of structure is described in Japanese unexamined Patent Publication No. 19516/1997.
The hand-stitched ball has the following advantages. The ball's air resistance is small, and its flying and gripping properties are excellent because the panel groove 6 is narrow and deep, being approximately 2.5 mm and 2 mm respectively. Tactility is soft, and controllability is good because the reinforcing layer is made of fabrics. Hence, the hand-stitched balls are used in ball games in great quantities.
However, a hand-stitched ball can not be stitched using a sewing machine because of the three-dimensionality of the sphere and the thick and hard complex panels reinforced by the liner material. Therefore, the operators are required to have substantially the same familiarity and skills, otherwise the balls manufactured by different operators will have large differences. Moreover, there are the problems of low production efficiency, unstable quality and unacceptable differences in weight, size and sphericity because of the hand-stitching process.
FIG. 4 illustrates a machine-stitched ball. A machine-stitched ball, whose skin layers are stitched using machinery, has a structure that combines the structures of the laminated ball and the stitched ball. In particular, the bladder 2 and the reinforcing layer 3 have the same structures as the above-mentioned laminated ball, with a reinforcing layer 3 being used to maintain the spherical shape and ensure durability. The marginal edges of the leather panels 4 are folded inward, and the leather panels 4 with the marginal edges are stitched together with machine-threads 8 (about 500-denier) into a spherical shape to form the skin layer. Then the integrated bladder 2 and reinforcing layer 3 are accommodated in the skin layer. In this example, the leather panel 4 is made of the complex lamination leather comprising a TPU film (with a thickness of 0.10-0.50 mm) and an EVA foam (with the thickness of 1.0-5.0 mm), or made of artificial leather (with a thickness of 1.0-3.0 mm).
A machine-stitched ball with the above structure is described in U.S. Pat. No. 5,772,545. In a machine-stitched ball, being different from the hand-stitched ball, the liner material is not required on the back of the leather panels 4 because a reinforcing layer 3 exists on the bladder 2, so that the leather panels 4 are so soft that they can be stitched using a sewing machine.
The machine-stitched ball can be produced in a mechanized way according to the above-mentioned structure and manufacturing method, so that machine-stitched balls have good quality, small errors in size and weight, and excellent durability.
However, machine-stitched balls have the following disadvantages. FIG. 4 shows a stitched portion of the leather panels 4. The stitched portion is lifted up by the reinforcing layer 3 attached to the bladder 2, so that the leather panels 4 at this place become flat, thus, the sphericity of the ball is impaired. Therefore, the ball has irregular bounce and poor flying properties, it can not be used as an official ball for a ball game.
In order to solve the above-mentioned problems of the prior art, international patent publication No. W099/61114 discloses a solution (see FIGS. 5 and 6). This invention relates to the laminated ball shown in FIG. 2, and has the same reinforcing layer 3 and bladder 2 as the laminated ball, characterized in that a complex panel 9 with the following structure is used as the leather panel.
As described in the description of the invention, a peripheral edge portion of the leather panel 4 with a thickness of 1.6-1.8 mm is folded in at a 90° (or 180°) angle, and the height difference due to this fold is eliminated by attaching a thickness adjusting member 10 with the thickness substantially equal to the height difference on the lower portion of the step (see FIG. 5).
The manufacturing method of the invention is described in detail in the description of this patent. That is, the leather panel 4 with the specified size (see FIG. 6(a)) and a thickness adjusting member 10 smaller than the leather panel 4 (see FIG. 6(b)) are cut, adhesive 11 (natural latex or adhesives of CR or PU series) is applied on the back side of the leather panel 4 and the lower surface of the thickness adjusting member 10, and both the panel 4 and member 10 are laminated together, as shown in FIG. 6(c). In this example, the adhesive is applied on the lateral side 15 of the thickness adjusting member 10 also. According to the above steps, a folding portion 12, which can cover the lateral side 15 of the thickness adjusting member 10, is formed along the entire periphery of the leather panel 4.
After the lamination is pressed into a mould 13, the folding portion 12 is folded further to cover the lateral side 15 of the thickness adjusting member 10 and then attached to it (see FIG. 6(d)).
Using the above-mentioned method, a complex panel 9 with a thickness of 2-10 mm can be obtained.
However, the invention on the basis of the thickness adjusting member 10 attached to the leather panel 4 has the following problems.
First, compared with other products, this ball is used under harsher conditions. That is, the football or volleyball is frequently and repeatedly subjected to impact over 100 kgf when kicked or spiked. All parts of the ball may stay in a damp state for a long time because of rain or sweat. When played outdoors, the ball is often used in sand or mud. Especially in the summer the ball often encounters a high temperature over 40° C. whether in use or in storage. All these conditions significantly affect the attached portions of the ball. Frequently the leather panels peel off. In order to solve the above problem, the development of an excellent attaching technique is a great challenge in the art.
The peeling off problem also exists in the above example. This peeling off phenomenon results from following two causes. First, the adhesive force between the thickness adjusting member 10 and the leather panel 4 can not always be kept constant, because the air remains in some places when they are laminated, resulting in unattached areas. Moreover, it is likely that the adhesive is excessively dried or is beyond the effective hours.
Second, the adhesive force between the folding portion 12 and the lateral side 15 of the thickness adjusting member 10 is weak. As is well known, a strong adhesive force results from the correct adhesive, proper temperature and strong engaging pressure. In the above invention, as shown in FIG. 6(d), the folding portion 12 folded in a 90° angle is just in contact with the lateral side 15 of the thickness adjusting member 10, so that there is no pressure toward the lateral side. This problem becomes especially obvious when the thickness adjusting member 10 is made from a buffering material like sponge. When detachment problem occurs at the folding portion 12, the folding portion 12 is separated from the lateral side 15 of the thickness adjusting member 10, which becomes the beginning of separation and the separation will be developed all over the leather panels 4.
Third, in the above invention, the adhesive must be coated on both the thickness adjusting member 10 and the leather panel 4, especially in the thickness adjusting member 10, the adhesive must be coated on the lateral side 15 one by one. This is inefficient and time-consuming, resulting in high manufacturing cost.
The present invention is directed to solve these problems. The present invention can reduce the adhered portions and significantly increase the strength of the adhered portions, while reducing the risk of detachment, so that the above-mentioned problems are solved. The manufacturing process of the ball panel is significantly simplified and the manufacturing cost is reduced.